A variety of types of software have recently been contrived in accordance with the remarkable spread of computers and can be utilized as general-purpose software irrespective of a type of computer. However, an illegal copy of software is increasing and thus some measures have to be taken immediately to prevent an illegal copy.
As one measure to prevent software from being illegally copied, there is provided a copy prevention method wherein a software is encrypted and only an authorized user is informed of a decrypting program and the encrypted software is decrypted before execution.
The conventional encryption is performed mainly using a software conversion algorithm. The more complicated the conversion algorithm, the more difficult the decryption of software, however, it is actually very hard to create such an encryption algorithm. Further, the conventional encryption method has drawbacks in which a decrypting program itself is copied and the encrypted software is decrypted and the decrypted program is copied and used, and so on.
Stated another way, the copy of the software is prevented in the conventional system by a software method using a password. However, the software method is not an almighty measure and can not perfectly prevent an illegal copy. It is possible to completely copy the software. The complete copy can not be distinguished from the original.
The present invention has been developed in consideration of the above and its object is to provide an encrypted program executing apparatus capable of preventing an encrypted program from being copied and used.